This Application is a U.S. National Phase Application of PCT International Application PCT/JP99/03197.
The present invention relates to a glass-ceramic composition, which can be sintered at low temperature and has high flexural strength. The invention also relates to electronic components and multilayer LC composite components using the glass-ceramic composition, these components having excellent electric characteristics at high frequency as well as excellent mounting reliability on a resin substrate, yet being easily manufactured.
With advancement of miniaturization and high frequency operation of electronic components used in the field of communications such as cellular phones, multilayer LC composite components, each carrying capacitors and coils integrated into a single component, have come to be used in late years. These multilayer LC composite components contain mutually connected capacitors and coils composed of internal electrodes provided in insulator layers constructed of glass-ceramic composition of low dielectric constant. For example, a circuit shown in FIG. 1 is composed internally as a multilayer LC composite component, as depicted in FIG. 2, FIG. 3, and FIG. 4. The multilayer LC composite component shown here is an example of low-pass filter, in which the circuit shown in FIG. 1 is obtained by forming capacitors C1 and C2, and a coil L with internal electrodes 2 through 5 provided in an insulator layer 1. Besides, there are external electrodes 6 through 9 formed on the exterior.
It is necessary to use a metal having high electrical conductivity, such as gold, silver, and copper, for the internal electrodes in order to improve a loss characteristic of multilayer LC composite components of this kind. However, since melting points of these metals are so low as approx. 960 degrees C. in the case of silver, for instance, a composition of the insulator needs to be such a material that can be fired densely even at a low temperature of around 900 degrees C. There has been developed for this purpose, a glass-ceramic composition sintered at a low temperature by mixing glass powder with ceramic powder of low dielectric constant, such as alumina (Al2O3), as a composite of insulator having a low relative dielectric constant and capable of being fired simultaneously with electrodes of high conductivity such as silver and copper.
As a nature of multilayer LC composite component, the surface area becomes wider compared to ordinary electronic component, and at the same time, it is required to be thin in height. This results in that a multilayer LC composite component tends to be large thin plate-like shaped. For this reason, a high mechanical strength is needed for an insulation body composed of glass-ceramic composition that constitutes the multilayer LC composite components. However, flexural strength of the glass-ceramic composition of the prior art is so low as less than 150 MPa in the case of a glass-ceramic composition for multilayer inductor described for instance in Japanese Patent No. 2597341, as compared with the ordinary ceramic such as alumina. In addition, there are often cases that coefficient of thermal expansion is generally so small as 7 ppm/K or less. This substantially increases a difference in coefficient of thermal expansion with respect to a substrate such as glass-epoxy resin (whose coefficient of thermal expansion is approx. 14 ppm/K in general), upon which the multilayer LC composite components are mounted, and thereby it tends to cause a defect such as a crack in an insulator layer due to a stress generated by heat in a soldering process and the like during mounting of the multilayer LC composite components on the resin substrate. According to a study of the inventors, it is desirable for the glass-ceramic composition constituting the insulator layer to have 150 MPa or greater in flexural strength and 9 ppm/K or greater in coefficient of thermal expansion in order not to reduce mounting reliability.
However, there are often cases that a softening point is lowered by adding a large amount of boric oxide (B2O3) or lead oxide (PbO) having an environmental problem, in order to make the glass-ceramic composition feasible for being fired at a low temperature around 900 degrees C. An oxide dielectric material described in Japanese Patent Examined Publication, No. H06-8189, for example, contains 4 to 12 wt. % of B2O3 in the entire glass-ceramic composition, and there is disclosed that it can not be sintered densely at 1000 degrees C. or less if the content is less than the above figure.
In the case of glass-ceramic composition with a high boric-oxide content, however, there may be instances where slurry can gelate unless water content in powder of the glass-ceramic composition is precisely controlled when mixing solvent and binder with powder of the glass-ceramic composition to turn it into the slurry in the manufacturing process of greensheets that constitute the multilayer body. This has been a big problem when forming the glass-ceramic composition that can be sintered at low temperature.
The present invention is intended to solve the above problem, and it aims at providing glass-ceramic composition and electronic components using the same, which are outstanding in mounting reliability particularly to a resin substrate since they have a large flexural strength and a moderately high coefficient of thermal expansion, and easy to manufacture because of a low content of boric oxide in the glass powder. It is also an object of the invention to provide multilayer LC composite components that are excellent in electric characteristics especially at high frequency since they carry internal electrodes of silver or copper having high electrical conductivity.
Glass-ceramic composition and an electronic component using the same of the present invention are constructed by forming and firing a mixture, which includes 55 to 65 wt. % of glass composite powder and 45 to 35 wt. % of forsterite (Mg2SiO4), wherein the glass composite powder includes 40 to 50 wt. % of SiO2, 30 to 40 wt. % of BaO, 3 to 8 wt. % of Al2O3, 8 to 12 wt. % of La2O3, and 3 to 6 wt. % of B2O3.
Also, another glass-ceramic composition and an electronic component using the same of the present invention are constructed by forming and firing a mixture, which includes 0.2 to 5 wt. % of oxidized copper calculated in CuO equivalent added further as a supplementary component into a 100% portion of another mixture of 50 to 65 wt. % of glass composite powder and 50 to 35 wt. % of forsterite (Mg2SiO4), wherein the glass composite powder includes 40 to 50 wt. % of SiO2, 30 to 40 wt. % of BaO, 3 to 8 wt. % of Al2O3, 8 to 12 wt. % of La2O3, and 3 to 6 wt. % of B2O3.
The glass-ceramic composition and the electronic components using the same, constructed as above, are outstanding in mounting reliability particularly to a resin substrate, since they have a thermal expansion coefficient of 9 ppm/K or greater and a flexural strength of 150 MPa or greater, and that they are easy to manufacture because of a low content of boric oxide in the glass powder.
Furthermore, the electronic component of the present invention has internal electrodes formed within the glass-ceramic composition described as above, the internal electrodes including at least one of gold, silver, and copper as the main component.
With the structure as described above, the electronic component of the present invention is superior in electric characteristics especially at high frequency, since it has the internal electrodes of silver or copper having high electrical conductivity.
In addition, a multilayer LC composite component of the present invention includes an insulator layer of the above-described glass-ceramic composition and internal electrodes made of silver or copper as the main component, and it further comprises a coil element formed of the internal electrodes in any configuration of a liner shape, a meander shape, and a spiral shape within the insulator layer, and a capacitor element formed of the internal electrodes confronting with each other across the insulator layer.
With the above structure, the multilayer LC composite component of the present invention is outstanding in mounting reliability particularly to a resin substrate since it has a thermal expansion coefficient of 9 ppm/K or greater and a flexural strength of 150 MPa or greater, it is easy to manufacture because of a low content of boric oxide in the glass powder, it results in a low dispersion of relative dielectric constant with respect to the firing temperature, and also it is superior in electric characteristics especially at high frequency, since it has the internal electrodes of silver or copper having high electrical conductivity.